1. Field of the Invention
The present invention relates to a key data input device, and more particularly, to a key-depression data input device such as a keyboard switch for use in a word processor, a personal computer, a terminal or other keyboard device.
2. Description of the Related Arts
In general, a key depression input device is constituted by rows of Y-direction conductor lines arranged in parallel and columns of X-direction conductor lines, these rows and columns forming a matrix, and key depression switches arranged at intersections of the Y-directions and X-direction conductor lines.
In the operation of the key-depression input device, the switches are scanned to determine the states thereof, and based on the result of the scanning, the data is input by the key depression input device.
In such a key-depression input device, when a plurality of keys are simultaneously or successively depressed, a by-pass conduction route may be formed to cause an intersection of an X line and a Y line which is not closed to appear to be closed. Such an apparently closed switch is called a phantom key or phantom switch.
Accordingly, a clock pulse is produced to detect the depression of keys and the repetition rate of the clock pulse is considerably shorter, under existing circumstances, than the time interval when the key is continuously depressed.
In a prior art, the keyboard is designed so that a plurality of keys cannot be depressed at the same time or continuously. Namely, when it is detected that a number of keys were depressed at the same time as mentioned above, this depression of the keys is considered invalid.
In order to improve the operability of the keyboard, a plurality of keys must be utilized efficiently, and in the case of a simultaneous depression of keys the case when a by-pass gives rise to a phantom depression keying must be distinguished from a case when this does not occur. The most simple and accurate means for handling a simultaneous depression of a plurality of keys is to provide diodes connected in series at each key contact.
When a diode connected in series is provided at each key contact, a phantom key depression state is usually avoided. Therefore, when three keys are depressed in sequence, the data for each key is produced, but since the number of diodes must be equal the number of key contacts, the volume of a switch board must be enlarged and the production line process more complicated, which leads to cost increases.
In the prior arts, it has been proposed, for example, that, in a key-depression input device, the rows and columns be scanned to detect the status of each switch, the detected information be stored in a storage, occurrences of the phantom switch condition in the switch array be determined, the status of the switches involved in the phantom switch condition be reversed, and after the termination of the phantom condition the key data be output.
However, in such a prior art key-depression input device the output of key data is fundamentally based on the existence/non-existence of the phantom switch condition, and an operation for detecting a key release manner, from the viewpoint of the key depression-release order among the keys involved in the phantom key condition, is not carried out. Therefore, the speed of output of the key data is limited, and is below a desired level, in such a prior art key-depression input device.